1. Field of the Invention
This invention relates to a closed loop vapor cycle refrigeration system, and more particularly to apparatus and method for improving refrigeration efficiencies by utilizing an expansion device in the evaporator section of the refrigeration system and by controlling the refrigerant flow through the evaporator.
2. Description of the Related Art
Expansion devices such as expansion engines have been used in the vapor cycle of refrigeration systems in an effort to improve the overall efficiency of such systems. For example, U.S. Pat. Nos. 3,934,424, 4,170,116, 4,086,772, 4,094,169 and 4,208,885 teach the use of an expansion engine in a vapor cycle to improve the overall efficiency of the refrigeration system. However, these and other prior art systems have failed to raise the system efficiency because these systems do not properly control the flow of the refrigerant through the evaporator; therefore, these systems have failed to gain commercial acceptance. Furthermore, the art in general has taught against the use of expansion engines in refrigeration systems. For example, David Mooney in the textbook, Mechanical Engineering states that "in actual cases, after allowing for the irreversibility of the real engine process, the gain by use of the expansion engine is usually negligible and such machines are not used in modern vapor refrigeration plants."
In a closed loop refrigeration system, potential energy is stored in the pressure difference of the refrigerant between the high pressure side and the low pressure side. Energy is wasted when this potential energy is changed into kinetic energy in the expansion valve of the refrigeration system. Also, energy is stored in the liquid refrigerant temperature on the high pressure side, which is changed into kinetic energy of the molecules when the liquid refrigerant boils in the evaporator. The prior art refrigeration systems attempt to improve the efficiency by utilizing this kinetic energy to drive or operate an expansion engine, which in turn is used to perform some useful function. However, the prior art systems do not overcome the energy waste because these systems do not properly control the expansion valve throttling process and the flow of the refrigerant through the evaporator.
The use of an expansion engine as taught in prior art systems, i.e., on an evaporator, produces an inherent conflict, which can be understood by considering the following two extremes of the flow of the refrigerant through the evaporator.
In the one extreme, if the refrigerant leaving the expansion engine is completely vaporized, there will be little refrigeration accomplished by the system.
In the other extreme, if liquid refrigerant is allowed to enter the compressors, unnecessary load will be placed on the expansion engine causing a loss of efficiency or mechanical failure,
The present invention addresses the above noted problems and provides a closed loop refrigeration in which improved efficiency is obtained by using a conventional expansion device such as an expansion engine or a novel expansion-compression-expansion valve in the evaporator and by controlling the refrigerant flow through the evaporator.